1. Field of the Invention
The present invention relates to a speed control apparatus for a hydraulic actuator which is built in an actuator such as a hydraulic motor, etc. and is attached to an outer portion of the same and is capable of adjusting a speed of an actuator by multiple steps, and in particular to a speed control apparatus for a hydraulic actuator In which is capable of dividing a load applied to a hydraulic actuator and adjusting a speed of the same based on a load condition of an actuator for thereby enhancing a responsive ability.
2. Description of the Background Art
FIG. 1 is a view illustrating a conventional speed control apparatus for a hydraulic actuator, and FIG. 2 is an enlarged view of a control valve of FIG. 1.
As shown therein, a speed control apparatus for a hydraulic actuator includes a hydraulic source(not shown) such as a hydraulic pump, etc., an actuator 1 which is connected with the hydraulic source and is rotated, stopped and reverse-rotated based on a supply state of an operation oil together with a hydraulic motor, a direction changing valve 2 which is switchably installed in a flow path between the hydraulic source and the actuator 1 for controlling a flowing direction of an operation oil supplied to the actuator 1, an inclination piston 3 for controlling an inclination angle of an inclination plate of the actuator 1, and a control valve 4 which is installed in a flow path between a parallel flow path 5 and the inclination piston 3 and is switched when a pilot signal Pi is applied and controls an operation oil supplied to the inclination piston 3.
In the drawing, reference character B represents a negative type brake apparatus for implementing an elastic biasing operation based on an initial state that the rotation of the actuator 1 is stopped, and R1 and R2 represent a relief valve for draining an operation pressure when an over load occurs in the actuator 1.
The operation of the above construction will be described.
In the speed control apparatus for a hydraulic actuator, as an operation pressure discharged from the hydraulic source(not shown) such as a hydraulic pump, etc. is supplied to the actuator 1 through the direction switching valve 2, the actuator 1 is rotated in the left or right direction. At this time, since the operation oil is not supplied to the inclination piston 3 which determines a speed of the actuator 1, the actuator is rotated at a low speed.
In the case that a pilot signal pressure Pi is supplied to the control valve 4 which is installed between the direction switching valve 2 and the inclination piston 3 based on an operation of a remote control valve(RCV: not shown), as shown in FIG. 1, since the control valve 4 is switched in the left direction, the operation oil discharged from the hydraulic source is supplied to the inclination piston 3 through the control valve 4. Therefore, the actuator 1 is rotated at a high speed by controlling the inclination angle of the inclination plate of the actuator 1.
At this time, in the case that the pressure of the operation oil which rotates the actuator 1 is above a set pressure, as shown in FIG. 1, the control valve 4 is rotated in the right direction, namely, is returned to the initial position, the operation oil supplied to the inclination piston 3 is disconnected, and the actuator 1 is rotated at a low speed.
However, the above described conventional speed control apparatus for a hydraulic actuator has the following problems.
Namely, in the conventional speed control apparatus for a hydraulic actuator, the speed of the actuator is determined to a low speed or a high speed based on a state that the operation oil discharged from the hydraulic source is supplied or not supplied to the inclination piston through the control valve. Therefore, the speed of the actuator 1 is adjusted based on only the two steps of a maximum and minimum steps. In the case that the pressure of the actuator 1 is set to a low state, the efficiency of the actuator 1 is decreased, and on the contrary, in the case that the same is set to a high state, an over load occurs in the actuator at a high speed operation, so that a durability is decreased, and a left span of the product is decreased.